The estranged wife of the prime suspect in the killing of Seattle federal prosecutor Thomas Wales testified Thursday before a federal grand jury investigating the 2001 slaying.

The woman, who married the suspect after the killing, is currently engaged in divorce proceedings with him.

She arrived at the U.S. Courthouse in Seattle shortly before 1 p.m. and was escorted into the grand-jury room by a federal security officer.

Grand-jury testimony is heard in secret, but she was called to bolster the testimony of a key witness who previously provided information to investigators, according to a source familiar with the case. She left the courthouse through a back exit.

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Wales, 49, was shot to death in his Queen Anne house on Oct. 11, 2001, while sitting at a computer in his basement. The assailant fired through a window from the backyard and fled in a vehicle parked nearby.

The suspect is a Bellevue airline pilot who had been prosecuted by Wales in a fraud case in 2000. He has been under investigation since shortly after Wales was killed. The Seattle Times is not naming him or his wife because he has not been charged in the case.

His wife had previously said she has no information directly implicating him in Wales’ killing.

But in court papers filed in her divorce case, she alleged that her husband stalked her during a prior separation, and that he had done the same thing with other women. She also alleged that he is “capable of anything.” In court papers, he denied stalking her and others.

The FBI has gathered other evidence that the pilot has stalked people, according to a source familiar with the case. Steven Clymer, special prosecutor in the case, declined comment before entering the grand-jury room Thursday.

The pilot and his wife began their relationship after Wales was killed. They were married in July 2005, and he filed for divorce in January.

The two lived in Snohomish until January. He has since moved back into a Bellevue house he has long owned.

His employment status is somewhat clouded, but he no longer works for one of his most recent employers, Virgin America, a new airline that is awaiting approval by the Federal Aviation Administration to begin flying.

A Virgin spokesman would not say why the company no longer employed the pilot, but said his departure was not part of larger layoffs.